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Speaker 1: Welcome to brain Stuff from how stuff works. Hey, brain stuff,

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Speaker 1: it's Christian Seger. Imagine you're waiting in line with hundreds

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Speaker 1: of other people to get Josh Clark from stuff you

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Speaker 1: should know as autograph. Your bodies start getting jammed together,

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Speaker 1: no longer being able to choose where to go. The

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Speaker 1: crowd begins acting like a fluid, and by that point

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Speaker 1: it's too late. You're in danger. People ignore the emergency exits,

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Speaker 1: creating a bottleneck and knocking one another over. You feel

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Speaker 1: pressure on all sides and you can't lift your arms.

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Speaker 1: You're pulled off your feet. Some people below you crawl

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Speaker 1: then die. Within three minutes, there are a hundred corpses

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Speaker 1: on the floor and you're struggling to breathe as the

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Speaker 1: air is squeezed out of your lungs. People generally try

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Speaker 1: to be decent and calm and behave rationally, except maybe

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Speaker 1: on YouTube comments. Even in a crisis, they'll try to

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Speaker 1: make safe decisions. But they can only do this based

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Speaker 1: on what they know, and crowds are a condition and

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Speaker 1: of everyday urban life, a necessary inconvenience of city living.

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Speaker 1: We pass in and out of them all the time

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Speaker 1: on subways and sidewalks. Crowd crushes, or also referred to

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Speaker 1: as crush accidents that killed ten or more people, have

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Speaker 1: happened on at least forty four recorded occasions since n

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Speaker 1: that's one every four months, and they happen everywhere. Multiple

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Speaker 1: crowd crushes have occurred with the Hajj in Mecca, Saudi Arabia,

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Speaker 1: where hundreds were killed on at least nine occasions. Much

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Speaker 1: of the information in this episode actually comes from an

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Speaker 1: excellent October article from The Guardian by Leo Benedictus. So

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Speaker 1: we've got two types of crowds to look at. The

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Speaker 1: first is low density, and it's the low risk type

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Speaker 1: of crowd, moving crowds with a density of up the

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Speaker 1: four people per square meter. Those are usually safe. People

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Speaker 1: have enough room then to decisions and act accordingly. But

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Speaker 1: the second type of crowd, those are high density crowds,

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Speaker 1: and they are high risk. There's been an increase in

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Speaker 1: the frequency of high density crowds lately because we're trying

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Speaker 1: to service more people in less time. High density crowds

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Speaker 1: are measured by at least six people per square meter.

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Speaker 1: Reports show that crowd disasters have more than doubled in

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Speaker 1: the past two decades. In the developed world, these are

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Speaker 1: most likely to occur at rock concerts and soccer games.

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Speaker 1: They also happen at religious events like the Hodge. One

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Speaker 1: of the best documented crowd disasters in the US happened

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Speaker 1: in nineteen seventy nine at a concert by The Who

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Speaker 1: in Cincinnati. High density crowds are a mass of complex

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Speaker 1: agents that respond based on their limited choices in their

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Speaker 1: exposure to products in their environment like heat. For instance,

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Speaker 1: physical contact in these high density crowds causes waves. Every

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Speaker 1: time there's physical contact between members. These shock waves can

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Speaker 1: lift people off their feet and even propel them about

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Speaker 1: three meters or ten feet. One researcher even studies mosh

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Speaker 1: pits by standing in the middle to witness crowd dynamics

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Speaker 1: produced by shock waves. Within high density crowds, there are

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Speaker 1: two types of dangers you want to watch out for.

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Speaker 1: Type one is what's referred to as progressive crowd collapse.

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Speaker 1: One person falls over and they deny their body as

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Speaker 1: something for the others to lean against. This creates a

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Speaker 1: domino effect where the adjacent people fall on top of

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Speaker 1: them or are knocked over trying to help. The hole

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Speaker 1: gets larger and more people are forced in and fall.

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Speaker 1: This often happens when a large crowd is moving steadily

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Speaker 1: through a confined route. Now, this actually happened to me

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Speaker 1: at a bouncing soul show in Luckily someone picked me

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Speaker 1: up and saved my life. Type two. The other one

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Speaker 1: you want to watch out for is the crowd crush.

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Speaker 1: When people are squeezed so much by a crowd that

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Speaker 1: they can't inflate their lungs, they'll die from compressive asphyxiation.

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Speaker 1: This typically happens when too many people push into a

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Speaker 1: confined area. Often those who die are the ones against

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Speaker 1: the wall. Now, maybe you've also heard talk of stampedes.

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Speaker 1: The mass media's idea of mass panic or a stampede

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Speaker 1: is actually misleading. Again, most of the evidence shows that

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Speaker 1: people take sensible action when they have their right information.

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Speaker 1: They're only crushed or crushing when they have no choice

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Speaker 1: in the matter and they don't know what's going on

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Speaker 1: because they're too far from the epicenter. Actually, stampedes themselves

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Speaker 1: are unlikely to kill you. The word stampede suggests that

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Speaker 1: people are causing havoc while they're running away, but the

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Speaker 1: real problem is when people can't move at all, but

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Speaker 1: train These events as mob psychology or crazes is. It's

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Speaker 1: misleading and it's false. Most people move in crowd patterns

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Speaker 1: and flows, but humans don't have the capability to transmit

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Speaker 1: information about the physical dynamics of their crowd the same

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Speaker 1: way ants can, for instance. Unfortunately, there isn't much of

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Speaker 1: a record of information in the crowd control industry to

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Speaker 1: provide analysis, but there are some technologies being developed to

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Speaker 1: try to help. In two thousand thirteen, a team of

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Speaker 1: UK and Saudi Arabia researchers developed an artificial intelligence system

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Speaker 1: that uses body heat readings to monitor the build up

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Speaker 1: of crowds and congestion. It uses infrared and black and

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Speaker 1: white images to interpret the crowds changing density. Then it

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Speaker 1: processes this information and acts like a human spotter, pointing

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Speaker 1: out high density crowd situations. Also in eleven, a German

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Speaker 1: researcher developed a system that observes when people sway slowly

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Speaker 1: from side to side to keep their balance. This is

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Speaker 1: another indicator of high density crowds. The system detects any

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Speaker 1: sudden increased in symmetrical movements that suggested as a congestion issue,

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Speaker 1: and it highlights the area in red, so you're probably

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Speaker 1: asking right now, what should I do if I'm in

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Speaker 1: a crowd disaster. There's some simple efforts that you can take.

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Speaker 1: Look ahead and listen to the crowds noise. If the

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Speaker 1: crowd starts to surge, wait for it, and then move

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Speaker 1: with it and sideways. Check out the brainstuff channel on YouTube,

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Speaker 1: and for more on this and thousands of other topics,

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Speaker 1: visit how stuff works dot com